The present invention relates to systems for controlling vibratory motors. More specifically, the present invention is directed to a method of and apparatus for monitoring the vibration amplitude of a vibratory feeder system by measuring the current and voltage utilized by the vibratory motor.
The vibratory feeders with which the present invention is to be used are well known in the art. In a typical construction of such a vibratory feeder, an electromagnetic vibrating motor is utilized in conjunction with a feed trough. The mass to be transported, such as coal or other bulky material, is moved along the feed trough by the action of the vibratory motor. Such electromagnetic vibrators suitable for use with this invention are described in commonly assigned U.S. Pat. Nos. 3,908,138 and 3,930,174, the disclosures of which are hereby incorporated by reference.
In order to control the action of a vibratory feeder, it is necessary to monitor and control the vibration and amplitude of the motor driving the feeder. Such monitoring and control results in a uniform capacity carried by the feeder and prevents overstroke of the electromagnetic vibrator itself. Such overstroke can cause self-destruction of the electromagnetic feeder.
As is well known, such vibratory feeders usually operate on the principle of resonance. By utilizing judicious design procedures, the mass M and spring rate K of the feeder are so proportioned that the resonant frequency of the vibratory feeder is close to its excitation frequency. This produces the minimum power requirement to operate the feeder.
However, during operation, both M and K may change. For example, the mass M might increase because of build-up of material on the deck of the feeder or the spring rate K might decrease because of higher environmental temperature conditions. These changes in M and K will result in a shifting of the system resonant frequency, thus causing an irregular or varying vibration amplitude.
Another source of irregularity may come from the line voltage, the fluctuation of which will vary vibration amplitude.
Heretofore, a motion transducer, such as an accelerometer or velocity pick-up, was installed on the vibration deck in order to aid in stabilizing the vibration amplitude. The transducer was connected by a cable to the controller of a regulatory feedback loop system. Such a feedback system is disclosed in U.S. Pat. No. 2,273,912. By monitoring the resonant frequency of the vibratory feeder, the vibration amplitude of the feeder could be modified to compensate for the changes in mass M and spring rate K. However, such an approach created substantial maintenance problems in that the environment surrounding the transducer was frequently filled with dust particles and other, larger solid particles. In addition, the constantly vibrating environment created additional instrumentation problems. Furthermore, the initial cost of the motion transducer and cable and the cost of maintaining both in proper operating condition in such a harsh environment was substantial.
Another prior art approach is to vary the frequency of vibration, as well as the vibratory current, in a closed loop control system, to regulate the amplitude of vibration, for instance, as shown in U.S. Pat. Nos. 3,447,051 and 3,748,583. However, it is likely to be costly to build and maintain such a complex system, especially relating to a large power vibrator where the need often arises to convey tens of thousands of tons of bulk materials per day.